Systems that detect the presence of a particular signal can be confused by the presence of interfering signals that are not of the modulation type that the system is attempting to detect. There are many types of interfering signals that could confuse a system. These can include wide-band interference such as thermal noise or spread-spectrum signals from cordless phones or wireless network devices. Other examples of interfering signals can include narrow-band signals such as harmonics of a digital clock source in a receiver, or hand-held radios.
One example of a system that commonly requires the ability to detect the presence of a particular signal of interest includes an intercept receiver. Intercept receivers provide an indication to a user that a signal of interest is present. It is important that the intercept receiver is not confused by signals that are not of interest because that would lead to false positives.